Virtual Placement Delete?

[Andrew Tomazos]

Please consider...

class B
{
virtual ~B() { ... }
}

class D : B
{
virtual ~D() { ... }
}

void f()
{
void* p = malloc(sizeof(D));
new (p) D; // ...placement new
B* b = (B*) p;
b->~B(); // ...is virtual destructor in effect?
free(p);
}

When f() is executed will D::~D() be called?

Thanks,
Andrew.

 

[Victor Bazarov]

Please consider...

class B
{
public:

virtual ~B() { ... }
} ;

class D : B

Need public inheritance to convert:
class D : public B

{
virtual ~D() { ... }
} ;

void f()
{
void* p = malloc(sizeof(D));
new (p) D; // ...placement new
B* b = (B*) p;

That's *not* a good idea. You should do

D* pd = new (p) D; // ...placement new
B* b = pd;

instead.

b->~B(); // ...is virtual destructor in effect?
free(p);
}

When f() is executed will D::~D() be called?

With your current cast from 'p' to a B*, the behaviour is undefined I'm
afraid.

V

 

[Andrew Tomazos]

That's *not* a good idea.  You should do

      D* pd = new (p) D; // ...placement new
      B* b = pd;

instead.



With your current cast from 'p' to a B*, the behaviour is undefined I'm
afraid.

(1) Can you tell me what the difference is between:

new (p) D;
B* b = (B*) p;

and

D* pd = new (p) D;
B* b = pd;

I would have thought they were equivalent? Why aren't they?

(2) If I use your recommended form, will the virtual destructor of
D::~D be called if I call b->~B() ?

Thanks,
Andrew.